The present invention relates to an optical monitoring system for semiconductor wafer processing and, more particularly, to the inclusion of an optical test device on the wafer surface that is capable of assessing the quality of various wafer processing steps.
There are a variety of high speed integrated circuit devices that are fabricated using wafers of, for example, Group III-V semiconductor material. Most commonly, these integrated circuits are formed on GaAs wafers. The processing steps in forming these devices include various fabrication techniques, including depositing layers of various other materials on the wafer surface and implanting dopants into the wafer. It is important that these doping and deposition processing steps be well-controlled in order to form devices with the desired characteristics in terms of speed, performance, etc.
One prior art technique for monitoring the process quality of these implant and layering processes consists of fabricating an electrical ring resonator test structure on the wafer along with the other integrated circuits. A problem with using an electrical ring resonator, however, is its speed limitations (MHz) as compared to the performance speed of the integrated circuits being fabricated (GHz-THz). Therefore, any test data that may be collected may not include sufficient resolution. Additionally, the electrical ring resonator is only activated subsequent to the device fabrication process (and, therefore, used to check the final performance characteristics of the devices under test), and cannot serve as a "real time" monitor for the various process steps.
Thus, a need remains in the art for an arrangement capable of providing real-time monitoring of the III-V device fabrication process at the speed needed (GHz-THz) for these devices.